This invention relates to fiber optic communication circuit components, and in particular, a fiber optic communication transceiver.
Fiber optic communication technology has been developing at a rapid pace. It has become apparent that fiber optic transmitters and receivers can be used in a wide variety of physical circuit topologies to improve the performance of existing networks or to create new fiber optic networks. The two major enabling features of fiber optic technology which promote its use in networking applications are its inherent/potential speed and the small size of the optical fiber in relation to metallic or wire media of equivalent bandwidth. As fiber optic networks have evolved, it has become a common practice to construct the network topology using a variety of multi mode coupler known as the star coupler in order to maximize the number of physical connections which may be made within the constraints of an optical power budget.
There are a number of applications wherein fiber optic networks are used, but wherein the number of fibers must be minimized. Examples of these occur in data transmission networks and aircraft, particularly fighter aircraft. Where the minimization of the number of fibers is important, a reflective star network topology is often selected, since it requires only half as many fiber connections to each node as would a transmissive star topology. In such arrangements, however, it is necessary to provide a means of physically connecting both the fiber optic transmitter and the fiber optic receiver to the same fiber. At this stage of the development of fiber optic technology, there are many types of optical couplers which theoretically could be used for such an application. Virtually all of these, however, present a physical size problem. This arises out of the fact that it has been found to be quite necessary to integrate the coupler within a transceiver housing having the fiber optic circuitry. The resulting package has generally been found to be objectionably large.
Assuming that these coupler packaging problems are solved, it is still necessary to develop fiber optic transmitter and receiver circuitry which is capable of satisfying the various requirements of the data network protocol. As a generalization, it can be said that it is necessary to be able to launch as much light as possible and to have as high a sensitivity as possible in order to provide the maximum optical power budget. It has been found that it would be desirable, if possible, to remove the necessity for including sophisticated clock circuity throughout the network and provide a way for retrieving a clock signal from the received data and to be able to lock into the optical signal with a minimum of preamble bits over a very wide optical power range.